Apparatus and procedures for continuous casting of metal ingots

ABSTRACT

In continuous casting of aluminum ingots by delivering molten metal downwardly to an axially vertical mold while withdrawing cast ingot continuously from the lower end of the mold, the supplied molten metal impinges against a baffle positioned immediately beneath the metal delivering tube in the mold. The major flow of molten metal impinges against a baffle positioned immediately beneath the metal delivering tube in the mold. The major flow of molten aluminum is directed laterally by the baffle, but a minor flow of the metal passes directly downward into the mold through a small central hole in the baffle, this hole being aligned with the mold axis.

ite States te ryson 5] June 27, 1972 s41 APPARATUS AND PROCEDURES FOR 3,459,346 8/1969 Tinnes ..222/DIG. 7 CONTKNUQUS CASTING 0F METAL 3,467,166 9/1969 Getselev et a1 ..164/82 x INGOTS [72] Inventor: Neil Burton Bryson, Kingston, Ontario,

Canada [73] Assignee: Alcan Research and Development Limited,

Montreal, Quebec, Canada [22] Filed: Sept. 25, 1970 [2!] Appl. No.: 75,561

[52] US. Cl ..164/82, 164/281 [51] Int. Cl ..B22d 11/10 [58] Field of Search ..l64/82,135,136, 281, 355, 164/337, 156; 222/DIG. 7

[56] References Cited UNITED STATES PATENTS 3,349,838 10/1967 Baier ..164/316 X Primary Examiner-R. Spencer Annear Attorney-Christopher C. Dunham, P. E. Henninger, Lester W. Clark, Robert S. Dunham, Gerald W. Griffin, Thomas F. Moran, Howard J. Churchill, R. Bradlee Boal and Robert Scobey [5 7] ABSTRACT In continuous casting of aluminum ingots by delivering molten metal downwardly to an axially vertical mold while withdrawing cast ingot continuously from the lower end of the mold, the supplied molten metal impinges against a baffle positioned immediately beneath the metal delivering tube in the mold. The major flow of molten metal impinges against a baffle positioned immediately beneath the metal delivering tube in the mold. The major flow of molten aluminum is directed laterally by the baffle, but a minor flow of the metal passes directly downward into the mold through a small central hole in the baffle, this hole being aligned with the mold axis.

5 Claims, 3 Drawing Figures API-ARATUS AND PROCEDURES FOR CONTINUOUS CASTING OF METAL INGOTS BACKGROUND OF THE INVENTION This invention relates to the continuous casting of metal ingots, and in a specific sense is directed to new and improved procedures and apparatus for continuously casting aluminum ingots, it being understood that the term aluminum" as herein employed embraces pure aluminum metal and alloys thereof.

In present-day commercial practice, the continuous casting of aluminum ingots (sometimes called direct chill casting) is effected in an axially vertical mold which is initially closed at its lower end by a downward movable platform or stool. Molten aluminum is introduced to the upper end of the mold, which is chilled by continuous supply of coolant fluid to its external surface, and as the molten metal solidifies in the region adjacent to the periphery of the mold, the stool is moved downward. With effectively continuous downward movement of the stool and correspondingly continuous supply of molten metal to the mold, there is produced an ingot of the desired length.

Commonly, the molten aluminum is supplied to the mold through a downwardly opening spout or dip tube, i.e., an axially vertical conduit aligned-with the mold axis, and having a lower end so positioned as to be immersed beneath the level of molten metal in the mold. The molten aluminum thus enters the mold along a downward vertical path. It has been found, however, that an entirely downwardly directed flow of molten aluminum, entering and mixing with the molten aluminum in the mold, tends to produce undesirable structural characteristics in the produced ingots. For this reason, a baffle structure is frequently disposed immediately beneath the lower end of the dip tube in the mold, to direct the delivered flow of aluminum metal laterally, i.e., toward the sides of the mold. Such baffle structure may be provided in the form of a float which rises and falls in correspondence with changes in level of mo]- ten aluminum in the mold, so as to engage and close off the lower end of the dip tube in the event that the molten metal level becomes excessively high; in other words, this float not only performs the baffle function just mentioned, but also serves to maintain the molten metal in the niold at substantially constant level throughout the casting operation. This level-controlling function is especially important for casting operations involving simultaneous delivery of molten aluminum to plural molds from a common supply.

Notwithstanding the improved characteristics achieved in continuous cast ingots by use of a baffle, it is found that these ingots are nevertheless still somewhat subject to center cracking, and tend to have a coarse feathery. or columnar grain structure providing an undesirable central core of coarse grains extending in the direction of casting of the ingot. In particular, these problems have necessitated use of relatively slow casting speeds for avoidance of center cracking. Also, such ingots exhibit areas of coarse cells.

To overcome the foregoing problems in the continuous casting of aluminum alloys, it is common practice to add to the alloy a grain refiner such as titanium, boron, or titanium diboride. The grain refiner addition affords substantial improvement in ingot structural characteristics, and effectively reduces center cracking. However, addition of grain refiner in amounts sufficient to achieve the desired results may cause inclusions that detract from the suitability of the ingot for particular applications e.g., production of bright-finished sheet); such use of grain refiner also adds to the cost of the casting operation and may present difficulties in handling of the mo]- ten metal prior to casting. Accordingly, in at least some instances, it would be desirable to omit some or all of the customary grain refiner addition from the metal to be cast without impairment of ingot structural characteristics. In other words, it would be desirable to provide continuous casting means and methods enabling production of an ingot characterized by fine equiaxed crystals throughout its length and cross section, and with substantial freedom from susceptibility to center cracking, even when the customary grain refiner content of the ingot is reduced or entirely omitted.

SUMMARY OF THE INVENTION The present invention in a broad sense embraces the discovery that by providing a small hole in the baffle structure positioned beneath the dip tube of continuous casting apparatus, grain refinement and indeed substantially complete elimination of coarse core grains and thereby a reduction of center cracking can be achieved in the produced ingots. The hole in the baffle is axially aligned with the mold, and serves to permit a minor flow of the introduced molten metal to pass directly downwardly into the center of the body of molten metal within the mold, while the major flow of molten metal is directed laterally toward the side walls of the mold by the baffle. The improved results thus attained, with respect to fineness of grain and freedom from center cracking in the cast ingots, are believed attributable to the fact that the minor flow of molten metal through the hole in the baffle creates a limited amount of turbulence in the center of the solidifying body of molten metal within the mold. In particular, the invention enables attainment of these advantageous results in ingots cast from aluminum alloys without addition of grain refiners to the alloys.

Thus, specifically, the invention contemplates the provision of apparatus for continuously casting metal ingots, including a mold having a wall defining an axially vertical casting zone with an open lower end; means for closing the lower end of the mold, positioned and adapted to support the lower extremity of an ingot being cast in the casting zone, and movable downwardly away from the mold for effecting continuous downward advance of the ingot during casting; means for delivering a flow of molten metal downwardly into an upper region of the casting zone; and means including a baffle positioned within the upper region of the zone in the path of downward advance of molten metal from the delivering means, for directing the downwardly advancing flow of molten metal laterally toward the mold wall, the baffle having a discharge lip spaced inwardly with respect to the wall of the mold so that the major flow of molten metal is directed downwardly beyond the bafile between the lip and the mold wall; wherein the improvement comprises the baffle having a small opening positioned centrally with respect to the periphery of the casting zone and dimensioned to permit a minor flow of molten metal to pass directly downwardly through the opening into the region of the casting zone below the baffle.

In this apparatus, the baffle may be provided by a float positioned in the casting zone immediately beneath the delivering means and adapted to rise and fall with change in level of molten metal in the casting zone, though restrained against substantial lateral movement relative to the delivering means; the bafile constitutes a portion of the float positioned in the path of downward advance of the molten metal from the delivering means. The small opening of the baffle is very preferably disposed in coaxial relation to the mold, so that the minor flow of molten metal passing downwardly through this opening is directed along the vertical axis of the mold. The delivering means or dip tube is also preferably axially aligned with the mold. In preferred embodiments of the invention, the area of the baffle opening is between about 3 percent and about 45 percent of the area of the discharge opening of the dip tube.

The invention further contemplates a method of continuously casting metal ingots including the steps of delivering molten metal in continuous downward flow into an upper region of an axially vertical casting zone of a mold wherein the molten metal collects and progressively solidifies to form an ingot, while directing the major portion of the downward flow laterally toward the side wall of the mold by interposing a baffle in the downward flow at the upper region of the casting zone, and while continuously drawing the ingot downwardly from the casting zone, wherein the improvement comprises directing a minor flow of the molten metal downwardly through the baffle into the region of the casting zone below the baffle along a path substantially coincident with the vertical axis of the casting zone.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a simplified sectional elevational view of a continuous casting apparatus embodying the present invention in a particular form;

FIG. 2 is a sectional view taken along the line 2 2 of FIG. 1, illustrating the baffle and float structure of the apparatus of FIG. 1; and

FIG. 3 is a further view of the baffle and float structure taken along the line 3 3 of FIG. 1.

DETAILED DESCRIPTION Referring to the drawing, there is shown in FIG. 1 a form of apparatus for continuously casting aluminum ingots, including an axially vertical annular mold (open at its lower end) to which molten aluminum metal 11 is supplied for casting an ingot 12. The mold l0, fabricated of metal (such as aluminum) suitably resistant to deterioration under the conditions for casting aluminum has a vertical inner wall 14 which defines an axially vertical casting zone 14a of desired horizontal cross section, e.g., circular, square, or rectangular), it being understood that this mold wall configuration determines the cross sectional shape of the produced ingot; merely by way of specific illustration, reference will be made herein to an annular mold wall 14 which is cylindrical, i.e., circular in cross section, for producing a cylindrical ingot.

Surrounding the outer surface of the mold wall 14 is a cooling jacket 15, shown for simplicity as formed of further wall portions cooperating with the wall 14 to define and enclose an annular chamber 150 completely laterally surrounding the casting zone. This enclosed chamber is supplied by suitable means (not shown) with a cooling fluid such as water for chilling the mold wall 14, and is preferably kept continuously filled with a flowing or circulating body of the fluid designated 16.

At the start of the casting operation, the lower end of the casting zone 14a is closed by a stool 18 which is carried on a platform 19 that is in turn supported on a hydraulic ram 20. As molten aluminum in the casting zone solidifies around the lower portion of the periphery of that zone, the stool l8 and platform 19 are drawn slowly vertically downward by operation of the hydraulic ram 20. The solidifying base of the ingot being cast, resting on the stool, then begins to emerge from the lower end of the casting zone.

The mold apparatus is arranged to direct a spray of cooling fluid onto the emerging solidified ingot surface immediately below the casting zone. Thus, as shown, there may be provided a slit 22 in the lower wall of the cooling jacket 15, extending entirely around the mold periphery, and oriented to direct water from the chamber a of the cooling jacket onto the surface of the emerging ingot. This spray of water, striking the ingot surface, acts to enhance the cooling and consequent solidification of the ingot as it moves downwardly away from the mold. In this arrangement, water is continually supplied to the chamber 15a and is continuously discharged through the slit 22 onto the ingot surface, so that there is a continuous flow of coolant fluid for removing heat from the solidifying metal.

Molten aluminum is supplied to the mold from a body or source shown as contained in a launder 26 positioned at a level above the mold and communicating therewith through an axially vertical dip tube 28 that extends downwardly from the launder into the casting zone 14a in coaxial relation to that zone. Very preferably, the lower end of dip tube 28 opens at a level in the casting zone somewhat beneath the level of the molten aluminum pool therein, to prevent surface turbulence in the casting zone pool. Avoidance of such turbulence is important, because a layer of aluminum oxide forms on the surface of the pool in the casting zone, and turbulence at the surface would tend to introduce this oxide as a contaminant into the ingot being cast.

Positioned in surrounding relation to the lower end of dip tube 28 and buoyantly supported in the pool of molten metal 11 in the casting zone is a float 30, comprising a relatively thick rigid disk-shaped body 31 having an axially vertical central bore 32 of sufficiently large diameter to accommodate the dip tube 28 with clearance. The lower surface of body 31 has a central recess 34, into which the bore 32 opens, substantially larger in cross sectional dimension than the bore. Extending across the recess 34, immediately beneath the bore 32 and spaced downwardly from the opening of bore 32 into recess 34, is a rigid baffle portion 36 of the float. This baffle portion, which may be formed integrally with or fixedly mounted on the body 31, is a straight-sided member, rectangular in vertical cross section, having an upper surface wider than the internal diameter of the dip tube 28. The baffle portion 36 is so positioned in relation to the bore 32 that when the dip tube 28 extends downwardly through bore 32, its open lower end is directly above the bafile. Thus, if the float 30 moves upward in relation to the dip tube until the baffle 36 engages the lower end of the dip tube, the baffle closes the lower end of the dip tube and molten metal cannot flow therefrom.

Further with reference to the structure of float 30, it will be understood that since the operating level of the molten metal pool 11 in the mold 10 is to be maintained above the lower end of the dip tube 28, and since the upper surface of the baffle 36 is ordinarily to be spaced downwardly from the dip tube lower end (to permit discharge of molten metal), the buoyant properties of the float should be such as to provide this desired spaced relation of dip tube and baffle when the molten metal is at the proper level in the mold. More specifically, the dimensions of the float should be so selected, in relation to the buoyancy of the material of which it is made, that the baflle is thus located in downwardly spaced relation to the dip tube when the float is supported by a molten metal pool at the desired operating level.

The float may be fabricated of any suitable material having appropriate buoyancy in molten aluminum, as well as being inert with respect to the molten aluminum and resistant to deterioration under the temperature and other conditions encountered in the casting operation. One example of a material of which the float may be made is the solid rigid composition of asbestos fiber and inorganic binder commercially available under the trade name Marinite.

Lateral movement of the float in relation to the dip tube and the mold is restricted within the range permitted by the limited clearance between the dip tube and the float bore 32. Upward movement of the float is, of course, restricted by engagement of the baffle portion 36 with the lower end of the dip tube. To limit downward displacement of the float, a pair of wire supports 38 are carried by the float, projecting vertically upward therefrom for a short distance above the upper rim of the mold, and bent laterally outward to project over the top wall of the mold at opposite sides thereof, so as to engage the mold top wall upon descent of the float to a pre-selected level and thereby to prevent downward movement of the float beyond such level. In the form shown, the supports 38 respectively extend through small vertical bores 40 provided on opposite sides of the float, and at their lower ends have enlarged heads 41 received in sockets at the lower ends of the bores to hold the supports in place relative to the float.

The foregoing structures as thus far described are generally conventional in character, for continuous casting of aluminum ingots, and the performance of casting operations with these structures will be readily apparent to one skilled in the art. Stated briefly, with the ram 20 positioned at the upper-most extremity of its vertical path of movement so that the stool 18 closes the lower end of the casting zone 14a, and with continuous supply of cooling water to the mold cooling jacket 15 for chilling the mold wall 14, molten aluminum supplied from the launder 26 flows downwardly by gravity through the dip tube 28 to fill the casting zone with the molten aluminum pool 11, to a desired level. As the chilling of the mold wall by the cooling water causes the lower peripheral portion of the molten aluminum pool, to solidify, at and adjacent to the mold wall in the lower portion of the casting zone, the hydraulic ram is moved slowly downward, drawing the stool 118 with it downwardly away from the mold. The solidifying cylindrical ingot body resting on the stool thus begins to emerge from the lower end of the mold, and comes into contact with sprays of cooling water discharged from the jacket I5 through slit 22. The exposure of the solidifying peripheral region of the ingot body to this spray of cooling water promotes solidification of interior of the body along an advancing front that extends inwardly from the periphery of the body until it finally reaches the center of the body, some distance below the mold.

In continuous casting operation, the ram 20 moves steadily downward at a predetermined rate of speed, drawing with it the solidified ingot which rests on the stool l8. Molten aluminum is supplied continuously downwardly through the dip tube 28 from the launder 26 to maintain the molten pool 11 in the mold 10 at a desired level. If the molten metal rises in the pool above this level, the baffle 36 engages the dip tube lower end, and retards further supply of molten aluminum to the mold until the continuing downward advance of the ingot from the mold has caused the molten aluminum pool to descend again to the desired level. In and below the mold in the ingot body being cast (which assumes the configuration of the cross section of the casting zone 14a, e.g., having as stated a circular cross section when wall 14 is similarly circular) there is a sump 24 of molten metal defined by the downwardly converging solidification front of the ingot; the sump is continuous with, and in effect constitutes the lower portion of, the molten metal pool 11 in the mold. Casting proceeds in this manner until an ingot of a desired length has been formed.

As will be seen, in the described casting operation, the mo]- ten metal entering the mold through the dip tube 28 initially flows vertically downward into the mold along a path coaxial with the casting zone 14a. However, before entering the sump portion 24, and indeed immediately below the lower end of the dip tube (which is somewhat below the level of molten metal in the mold) the entering flow of metal impinges against the upper surface of the baffle 36 and is thereby directed laterally toward the side walls of the mold, through the recess 34, finally descending into the sump 24 between the lips or edges of the baffle and the side wall of the mold in a more or less lateral direction, rather than vertically downward along the mold axis. In short, the entering flow of molten metal, though initially directed axially downward into the mold, follows a lateral flow path towards the side of the mold as it enters the sump, in accordance with known and conventional procedure.

As a particular feature of the present invention, there is provided in the baffle 36 a small opening 43, extending through the baffle from the upper to the lower surface thereof, this opening being axially vertical and axially aligned with dip tube 28 and with the casting zone 14a. The opening 43 is substantially smaller in cross sectional area than the internal cross section of the dip tube 28; preferably, the cross sectional area of opening 43 is between about 3 percent and about 45 percent of the dip tube internal cross sectional area.

The opening 43 permits a continuous minor flow of the molten aluminum entering pool 11 through dip tube 28 to pass directly downward into the sump portion 24 along the axis of the casting zone, throughout the duration of the casting operation, while the major flow of molten aluminum is still directed laterally, as in conventional practice, toward the side wall of the mold by baffle 36. The minor axially directed vertical downward flow of molten metal through opening 43 creates minor turbulence in the axial region of the molten metal sump 24. It is found that ingots produced with a float having such opening are characterized by superior grain refinement and the absence of a coarse, columnar central core, with concomitantly minimized tendency toward center cracking, i.e., as compared with ingots produced in casting apparatus having a float with conventional baffle lacking a small central hole.

It is presently believed that these improved results are attributable to some effect of the aforementioned minor turbulence in the sump, in preventing formation of coarse columnar or feathery grains along the core of the solidifying ingot, and thereby preventing formation of a coarse core structure that is susceptible to center cracking.

Provision of the small opening 43 in a baffle to some extent reduces the ability of the baffle to control discharge of molten metal from the dip tube; i.e., upon rise of metal level in the mold carrying the float bafile upward into closing engagement with the dip tube lower end, some molten metal still flows out of the dip tube through the opening 43. Nevertheless, the advantages of the invention may be achieved with a baffle opening small enough to permit a satisfactory degree of molten metal discharge control by the float.

By way of specific illustration, in one example of a float of the present invention fabricated of Marinite," and used for casting cylindrical aluminum ingots 6 inches in diameter, the external diameter of the disc-shaped float body 31 was 4% inches, and the maximum internal (horizontal) diameter of the recess 34 was 3 inches, with a 1% inch diameter bore 32 for the dip tube, and a distance of 1% inches between the upper surface of the disc-shaped body 31 and the upper surface of the baffle 36. The distance between the lower rim of bore 32 and the upper surface of baflle 36 was nine-sixteenths of an inch. The horizontal cross-sectional dimension of the baffle (as seen in FIG. 2), was 1% inches and the vertical thickness of the baffle was eleven-sixteenths of an inch. The vertical opening 43, centered in the baffle, was one-fourth inch in diameter. The dip tube with which this float was used had an internal diameter of three-fourths of an inch.

In further illustration of the method and apparatus of the invention, reference may be had to the following specific examples, wherein alloy compositions used are identified by Aluminum Association (AA) designations. The alloys cast in each of the examples did not contain any grain refiner additions, such as are conventionally used in the continuous casting art to reduce center cracking and related problems.

EXAMPLE I Six cylindrical ingots of AA 6063 aluminum alloy each 6 inches in diameter were continuously cast in a mold arranged generally as shown in FIG. 1. In casting one of the ingots, a baffle having a central vertical opening three-eighths inch in diameter was used, and in casting another of the ingots a baffle having a central vertical opening one-fourth inch in diameter was used. The remaining four ingots were cast with conventional float baffles having no central opening. During casting, it was found that the float having the one-fourth inch opening provided normal level control of molten metal in the mold, but the float having a three-eighths inch opening presented some difficulty in level control.

All four ingots cast with conventional floats having no baffle opening exhibited severe center cracking. The ingot cast with a float baffle having a three-eighths inch opening had no center cracking, and the ingot cast with a baffle having a onefourth inch opening exhibited a small intermittent center crack.

Ingots cast with the conventional float baffles having no opening were found to have a coarse columnar structure with large patches of feathery grains. The structure of the ingot cast with the float baffle having a one-fourth inch hole included an outer rim of equiaxed grains with an inner area of fine columnar grains. The ingot cast with a float having a three-eighths inch baffle opening had a structure of fine equiaxed grains throughout its cross section.

EXAMPLE II In the casting of 6 inch diameter cylindrical ingots of an aluminum alloy having the Aluminum Association designation EC, at a casting speed of 7 inches per minute, it was found that ingots cast using a float baffle having a small vertical central opening in accordance with the present invention were characterized by a much finer grain structure than those cast with a conventional baffle having no central opening. The ingots cast with a baffle having an opening had no central core, and were free of center cracking. ln casting further 6 inch diameter ingots of the same alloy at a speed of 9% inches per minute and an initial molten metal temperature of 685 C., again using a float bafi'le having a small central opening in accordance with the invention, i found that internal defects were reduced by a factor of approximately three as compared with ingots cast of the same alloy under comparable conditions, but using a conventional float baffle having no opening. No increase in porosity or dross content was observed in the ingots cast with the baffle having a central opening.

EXAMPLE lll Satisfactory cylindrical ingots of EC aluminum alloy 5% inch in diameter were cast at a speed of 13%. inches per minute using a float bafile having a small vertical central opening in accordance with the invention.

EXAMPLE IV Six inch diameter cylindrical ingots of AA 1285 aluminum alloy, cast at a speed of 6 inches per minute and an initial molten metal temperature of 685 C., using a float baffle having a small vertical central opening in accordance with the invention, were found to exhibit considerably reduced center cracking as compared with ingots of the same alloy cast under like conditions but using a float having a conventional baffle with no opening.

EXAMPLE V A plurality of cylindrical ingots of AA-6463 alloy 6 inches in diameter were cast at a speed of 6 inches per minute. The first of these ingots was cast using a conventional float bafile having no central opening, and subsequent ingots were cast using, in succession, float baffles having vertical central openings respectively one-eighth inch, three-sixteenths inch, one-fourth inch, five-sixteenths inch and three-eighths inch in diameter. A final ingot was cast using no float, i.e., permitting free discharge of the entire flow of molten metal directly downward from the dip tube into the mold.

Upon examination, it was found that the ingots exhibited a generally decreasing grain size as the diameter of the float baffle opening was increased from one-eighth inch to five-sixteenths inch. Difficulty in controlling molten metal level in the mold was encountered with the floats having a five-sixteenths inch and a three-eights inch baffle opening. Little grain refinement was observed in the ingots cast with a float having a oneeighth inch opening, as compared with the ingots cast using a conventional float having no opening.

Ultrasonic and visual inspection of the ingots revealed that the ingot cast with a conventional float and that cast with the float having a one-eighth inch opening exhibited center cracking. No center cracking was found in the other ingots. It has been found that the maximum casting speed that may be used for ingots of the same dimensions and alloy, without center cracking, is 4% inches to 4% inches per minute as contrasted with the 6 inch per minute casting speed used in the present example.

EXAMPLE Vl Two ingots of AA-6063 aluminum alloy were cast at a speed of 6 inches per minute. One of these ingots was cast with a float having a vertical central baffle opening one-fourth inch in diameter and the other with a conventional float having no baffle opening. The ingot cast with a float having a baffle opening in accordance with the invention, exhibited a fine equiaxed grain structure in its peripheral region with a structure of fine columnar grain 2 inches in diameter at the center of the ingot, while the ingot cast with a conventional float had coarse columnar and feathery grains. Also, the ingot cast with the float having a baffle opening was free from center cracking, while center cracking was present in the ingot cast with the conventional float. On microscopic examination, the ingot cast with the conventional float was found to have many patches of very coarse cells surrounded by fine cells, and was characterized by nonuniformity of cell size and twinning. The ingot cast with the float having a baf'fle opening had very few patches of coarse cells, exhibiting primarily fine cells; the cell size was substantially uniform except for rare patches of large cells; and twinning was absent.

I claim:

1. Apparatus for continuously casting metal ingots, includa. a mold having a wall defining an axially vertical casting zone with an open lower end;

b. means for closing the lower end of said mold, said means being positioned and adapted to support the lower extremity of an ingot being cast in said zone, and being movable downwardly away from said mold for effecting continuous downward advance of the ingot during cast- 8;

c. means for delivering a flow of molten metal downwardly into an upper region of said casting zone; and

d. means, including a baffle positioned within the upper region of said zone in the path of downward advance of molten metal from said delivering means, for directing the downwardly advancing flow of molten metal toward the wall of the mold, said baffle having a discharge lip spaced inwardly with respect to the wall of the mold so that the major flow of molten metal is directed downwardly beyond the baffle between said lip and said mold wall;

wherein the improvement comprises e. said baffle having a small opening substantially axially aligned with said casting zone and dimensioned to permit a minor flow of molten metal to pass directly downward through said opening into the region of said zone below said bafile.

2. Apparatus for continuously casting metal ingots, includa. a mold having a wall defining an axially vertical casting zone with an open lower end;

b. means for closing the lower end of said mold, said means being positioned and adapted to support the lower extremity of an ingot being cast in said zone, and being movable downwardly away from said mold for effecting continuous downward advance of the ingot during castmg;

c. means for delivering a flow of molten metal downwardly into an upper region of said casting zone; and

d. a float positioned in said casting zone immediately beneath said delivering means and adapted to rise and fall with change in level of molten metal in said zone, but restrained against substantial lateral movement relative to said delivering means, said float having a baffle portion positioned in the path of downward advance of molten metal from said delivering means, for directing the downwardly advancing flow toward the wall of the mold, said baffle portion having a discharge lip spaced inwardly with respect to the mold wall so that the major flow of molten metal is directed downwardly beyond the float between said discharge lip and said mold wall;

wherein the improvement comprises e. said baffle portion having a small opening substantially axially aligned with said casting zone and dimensioned to permit a minor flow of molten metal to pass directly downward through said opening into the region of said zone below said baffle portion.

a. a mold having a wall defining an axially vertical casting zone with an open lower end;

b. means for closing the lower end of said mold, said means being positioned and adapted to support the lower extremity of an ingot being cast in said zone, and being movable downwardly away from said mold for effecting continuous downward advance of the ingot during castmg;

C. a molten metal delivery tube having a downwardly directed opening disposed substantially in concentric relation to said casting zone in an upper region of said zone for discharging molten metal downwardly into said zone; and

d. a float, positioned in said casting zone immediately beneath said delivery tube opening and adapted to rise and fall with change in level of molten metal in said zone, but restrained against substantial lateral movement relative to said delivery tube, said float having a central baffle portion shaped and positioned to close said tube opening upon rise of said float into engagement with said tube in correspondence with rise of molten metal in said zone to a predetermined level, said bafi'le portion being further positioned and adapted to direct the downwardly advancing flow of molten metal toward the wall of the mold, said baffle portion having a discharge lip spaced inwardly with respect to the mold wall so that the major flow of molten metal is directed downwardly beyond the float between said discharge lip and said mold wall;

wherein the improvement comprises e. said baffle portion having a small opening positioned substantially in concentric relation to said casting zone and dimensioned to permit a minor flow of molten metal to pass directly downward through said opening into the region of said casting zone below said baffle portion.

4. Apparatus as defined in claim 3, wherein said small opening of said bafile portion has a cross sectional area equal to between about 3 percent and about 45 percent of the internal cross sectional area of said delivery tube.

5. A method of continuously casting metal ingots including the steps of a. delivering molten metal in continuous downward flow into an upper region of an axially vertical casting zone of a mold wherein said molten metal collects and progressively solidifies to form an ingot, while b. directing the major portion of said downward flow at said upper region of said casting zone laterally toward the side wall of said mold by interposing a baffle in said downward flow at said upper region of said zone and while c. continuously drawing said ingot downwardly from said casting zone,

wherein the improvement comprises d. directing a minor flow of said molten metal downwardly through said baffle into the region of said casting zone below said baffle along a path substantially coincident with the vertical axis of said casting zone. 

1. Apparatus for continuously casting metal ingots, including a. a mold having a wall defining an axially vertical casting zone with an open lower end; b. means for closing the lower end of said mold, said means being positioned and adapted to support the lower extremity of an ingot being cast in said zone, and being movable downwardly away from said mold for effecting continuous downward advance of the ingot during casting; c. means for delivering a flow of molten metal downwardly into an upper region of said casting zone; and d. means, including a baffle positioned within the upper region of said zone in the path of downward advance of molten metal from said delivering means, for directing the downwardly advancing flow of molten metal toward the wall of the mold, said baffle having a discharge lip spaced inwardly with respect to the wall of the mold so that the major flow of molten metal is directed downwardly beyond the baffle between said lip and said mold wall; wherein the improvement comprises e. said baffle having a small opening substantially axially aligned with said casting zone and dimensioned to permit a minor flow of molten metal to pass directly downward through said opening into the region of said zone below said baffle.
 2. Apparatus for continuously casting metal ingots, including a. a mold having a wall defining an axially vertical casting zone with an open lower end; b. means for closing the lower end of said mold, said means being positioned and adapted to support the lower extremity of an ingot being cast in said zone, and being movable downwardly away from said mold for effecting continuous downward advance of the ingot during casting; c. means for delivering a flow of molten metal downwardly into an upper region of said casting zone; and d. a float positioned in said casting zone immediately beneath said delivering means and adapted to rise and fall with change in level of molten metal in said zone, but restrained against substantial lateral movement relative to said delivering means, said float having a baffle portion positioned in the path of downward advance of molten metal from said delivering means, for directing the downwardly advancing flow toward the wall of the mold, said baffle portion having a discharge lip spaced inwardly with respect to the mold wall so that the major flow of molten metal is directed downwardly beyond the float between said discharge lip and said mold wall; wherein the improvement comprises e. said baffle portion having a small opening substantially axially aligned with said casting zone and dimensioned to permit a minor flow of molten metal to pass directly downward through said opening into the region of said zone below said baffle portion.
 3. Apparatus for continuously casting metal ingots, including a. a mold having a wall defining an axially vertical casting zone with an open lower end; b. means for closing the lower end of said mold, said means being positioned and adapted to support the lower extremity of an ingot being cast in said zone, and being movable downwardly away from said mold for effecting continuous downward advance of the ingot during casting; c. a molten metal delivery tube having a downwardly directed opening disposed substantially in concentric relation to said casting zone in an upper region of said zone for discharging molten metal downwardly into said zone; and d. a float, positioned in said casting zone immediately beneath said delivery tube opening and adapted to rise and fall with change in level of molten metal in said zone, but restrained against substantial lateral movement relative to said delivery tube, said float having a central baffle portion shaped and positioned to close said tube opening upon rise of said float into engagement with said tube in correspondence with rise of molten metal in said zone to a predetermined level, said baffle portion being further positioned and adapted to direct the downwardly advancing flow of molten metal toward the wall of the mold, said baffle portion having a discharge lip spaced inwardly with respect to the mold wall so that the major flow of molten metal is directed downwardly beyond the float between said discharge lip and said mold wall; wherein the improvement comprises e. said baffle portion having a small opening positioned substantially in concentric relation to said casting zone and dimensioned to permit a minor flow of molten metal to pass directly downward through said opening into the region of said casting zone below said baffle portion.
 4. Apparatus as defined in claim 3, wherein said small opening of said baffle portion has a cross sectional area equal to between about 3 peRcent and about 45 percent of the internal cross sectional area of said delivery tube.
 5. A method of continuously casting metal ingots including the steps of a. delivering molten metal in continuous downward flow into an upper region of an axially vertical casting zone of a mold wherein said molten metal collects and progressively solidifies to form an ingot, while b. directing the major portion of said downward flow at said upper region of said casting zone laterally toward the side wall of said mold by interposing a baffle in said downward flow at said upper region of said zone and while c. continuously drawing said ingot downwardly from said casting zone, wherein the improvement comprises d. directing a minor flow of said molten metal downwardly through said baffle into the region of said casting zone below said baffle along a path substantially coincident with the vertical axis of said casting zone. 